1. Field of the Invention
The present invention relates to magnetic inks and more particularly to an aqueous magnetic ink composition and a method for making an aqueous magnetic ink character recognition (MICR) ink for use in desktop inkjet printers.
2. Description of Related Art
Magnetic Ink Character Recognition (MICR) is a printing technology used primarily in the banking and financial services markets. The process of MICR encoding involves the printing of magnetically readable characters. These characters are printed using methods such as impact printing (MICR ribbons), electrophotographic printing (MICR toner) and traditional offset printing (MICR ink). More recently, MICR printing has been attempted using inkjet technology.
The printing of MICR characters using inkjet printing presents unique challenges, such as sufficient suspension of magnetic material in a fluid, adequate ink drying, and successful permanence or adhesion of the MICR ink to a given substrate.
MICR inkjet ink requirements include high pigment loadings in the ink to achieve an acceptable MICR signal level. Desktop inkjet printers require low viscosity inks. Providing a low viscosity ink with sufficient magnetic pigment loading to produce acceptable MICR signal levels, present a significant challenge.
Prior art MICR inks for inkjet printers have failed to create an ink that is stable enough for use in desktop inkjet printers and have the required minimum magnetic resonance.
U.S. Pat. No. 6,767,396, granted Jul. 27, 2004, is directed to a process for making an aqueous MICR inkjet ink that uses surfactants and grinding of iron oxide particles, the only achieving a peak magnetic resonance of about 20 emu/g.
U.S. Pat. No. 6,746,527, granted Jun. 8, 2004, is directed to an aqueous MICR inkjet ink composition which uses a combination of surfactants, an anionic surfactant and a nonionic surfactant for dispersion of the iron oxide particles.
U.S. Pat. No. 6,726,757, granted Apr. 27, 2004, is directed to an aqueous MICR inkjet ink composition that coats the iron oxide particles with a hydrophobic coating to aid in dispersion of the particles.
U.S. Pat. No. 7,255,433, granted Aug. 14, 2007, is directed to a multiple pass inkjet printing process using the aqueous MICR inkjet ink discussed in the above patents. The process requires laying down at least two layers of the MICR inkjet ink to achieve the minimum signal load required by the ANSI standard.
Accordingly, there is a need for a magnetic ink composition and a method of making a low viscosity MICR inkjet ink suitable for use in desktop inkjet printers.